1. Field of the Invention
The present invention relates to a liquid driver system, specifically to a liquid driver system utilizing induced-charge electroosmosis applicable as a pumping system or the like.
2. Description of the Related Art
Micro-pumps utilizing electroosmosis are used in application fields such as a μTAS (micro-total analysis system) since the micro-pump has a relatively simple structure containing no moving member and can be installed in a minute flow channel.
Recently, the micro-pumps utilizing induced-charge electroosmosis are attracting attention because the pumps are capable of driving a liquid at a high flow rate and preventing a chemical reaction between the electrode and the liquid by AC driving.
U.S. Pat. No. 7,081,189, and M. Z. Bazant and T. M. Squires: Phys. Rev. Lett. 92, 066101 (2004) disclose pumps utilizing the induced-charge electroosmosis (ICEO).
The pumps disclosed include: (1) a half-coat type ICEO pumps which control the liquid flow by adjusting the region of charge induction in a metal post by an electric field by coating a half of the metal post between the electrodes with a dielectric thin film; and (2) an asymmetric metal post type ICEO pump which controls a flow of the liquid in a fixed direction by placing a metal post having a triangular or other asymmetric shape between the electrodes.
The half-coat type ICEO pump (1) disclosed in the above U.S. Patent and the reference document (Phys. Rev. Lett.) needs formation of a dielectric film for masking partially the metal post, which increases the number of steps of the production process, and increases the number of the mask sheets. Therefore, another approach is necessary for production of the system having a higher performance at a lower cost.
The asymmetric post type ICEO pump (2) controls the liquid flow in a certain direction as a whole by improving the shape of the metal post. However, the simple improvement only of the shape of the post tends to cause inevitably a liquid flow in a reverse direction in addition to the normal forward direction. Therefore, by limiting the reverse flow, the flow rate of the liquid discharged from the pump can be increased more.